//==================================================================
/// DUtils_Random.cpp
///
/// Created by Davide Pasca - 2010/6/16
/// See the file "license.txt" that comes with this project for
/// copyright info. 
//==================================================================

#include "DUtils_Random.h"

//==================================================================
namespace DUT
{

//==================================================================
RandMT::RandMT()
{
	seedMT(1U);
}

//==================================================================
RandMT::RandMT(U32 seed)
{
	seedMT(seed);
}

//==================================================================
void RandMT::seedMT( U32 seed )
{
	//
	// We initialize state[0..(N-1)] via the generator
	//
	//   x_new = (69069 * x_old) mod 2^32
	//
	// from Line 15 of Table 1, p. 106, Sec. 3.3.4 of Knuth's
	// _The Art of Computer Programming_, Volume 2, 3rd ed.
	//
	// Notes (SJC): I do not know what the initial state requirements
	// of the Mersenne Twister are, but it seems this seeding generator
	// could be better.  It achieves the maximum period for its modulus
	// (2^30) iff x_initial is odd (p. 20-21, Sec. 3.2.1.2, Knuth); if
	// x_initial can be even, you have sequences like 0, 0, 0, ...;
	// 2^31, 2^31, 2^31, ...; 2^30, 2^30, 2^30, ...; 2^29, 2^29 + 2^31,
	// 2^29, 2^29 + 2^31, ..., etc. so I force seed to be odd below.
	//
	// Even if x_initial is odd, if x_initial is 1 mod 4 then
	//
	//   the          lowest bit of x is always 1,
	//   the  next-to-lowest bit of x is always 0,
	//   the 2nd-from-lowest bit of x alternates      ... 0 1 0 1 0 1 0 1 ... ,
	//   the 3rd-from-lowest bit of x 4-cycles        ... 0 1 1 0 0 1 1 0 ... ,
	//   the 4th-from-lowest bit of x has the 8-cycle ... 0 0 0 1 1 1 1 0 ... ,
	//    ...
	//
	// and if x_initial is 3 mod 4 then
	//
	//   the          lowest bit of x is always 1,
	//   the  next-to-lowest bit of x is always 1,
	//   the 2nd-from-lowest bit of x alternates      ... 0 1 0 1 0 1 0 1 ... ,
	//   the 3rd-from-lowest bit of x 4-cycles        ... 0 0 1 1 0 0 1 1 ... ,
	//   the 4th-from-lowest bit of x has the 8-cycle ... 0 0 1 1 1 1 0 0 ... ,
	//    ...
	//
	// The generator's potency (min. s>=0 with (69069-1)^s = 0 mod 2^32) is
	// 16, which seems to be alright by p. 25, Sec. 3.2.1.3 of Knuth.  It
	// also does well in the dimension 2..5 spectral tests, but it could be
	// better in dimension 6 (Line 15, Table 1, p. 106, Sec. 3.3.4, Knuth).
	//
	// Note that the random number user does not see the values generated
	// here directly since reloadMT() will always munge them first, so maybe
	// none of all of this matters.  In fact, the seed values made here could
	// even be extra-special desirable if the Mersenne Twister theory says
	// so-- that's why the only change I made is to restrict to odd seeds.
	//
	initseed = seed;

	U32 x = (seed | 1U) & 0xFFFFFFFFU, *s = state;
	int    j;
	left = 0;
	for(*s++=x, j=N; --j; *s++ = (x*=69069U) & 0xFFFFFFFFU);
}

//==================================================================
U32 RandMT::reloadMT()
{
	U32 *p0=state, *p2=state+2, *pM=state+M, s0, s1;
	int    j;

	if(left < -1)
		seedMT(initseed);

	left=N-1, next=state+1;

	for(s0=state[0], s1=state[1], j=N-M+1; --j; s0=s1, s1=*p2++)
		*p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);

	for(pM=state, j=M; --j; s0=s1, s1=*p2++)
		*p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);

	s1=state[0], *p0 = *pM ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
	s1 ^= (s1 >> 11);
	s1 ^= (s1 <<  7) & 0x9D2C5680U;
	s1 ^= (s1 << 15) & 0xEFC60000U;
	return(s1 ^ (s1 >> 18));
}

//==================================================================
#if !defined(DUT_USE_CHEAP_RANDOM)

RandMT _gsRandMT;

#else

//==================================================================
u_int _g_m_w = 111;
u_int _g_m_z = 222;

#endif

//==================================================================
}
